Hello, I get the same result. I believe it is because one of the angles in your tetrahedron is acute, which would not be the case for a chemical entity.
Best wishes, Jon Cooper (Emeritus at UCL) [email protected] Erratum and other hopefully useful things: https://crxp.org.uk Sent with [Proton Mail](https://proton.me/mail/home) secure email. On Thursday, 12 February 2026 at 08:14, Matthias Ullmann <[email protected]> wrote: > Dear all, > > I have a question about the chiral volume and a potential error on this ccp4 > website: > > https://www.ccp4.ac.uk/html/refmac5/theory/chiral.html > > On this website, it is stated: > > ======================== > > Procedure to find the sign of a chiral > centre[¶](https://www.ccp4.ac.uk/html/refmac5/theory/chiral.html#procedure-to-find-the-sign-of-a-chiral-centre) > > - > > Put atom1 and draw bonds from the centre (atom1) to atom2, atom3, atom4 as in > figure 3. When the eye goes from atom2 to atom4 it should travel clockwise. > > - > > Assuming that atom2, atom3, atom4 are in the plane of the picture, then if > atom1 is below the plane, the chiral volume sign is plus, and otherwise it is > minus. If the numbering is based on the sequence rules, a positive chiral > volume corresponds directly to R and negative to S > > ======================== > > The equation to calculate the chiral volume is usually defined as > > V = ⅙ (r2-r1) [(r3-r1)x(r4-r1)] > > If I do the calculation, I get other results. Here is an example: > > X1 0.0 0.0 0.0 > > X2 0.0 1.0 1.0 > > X3 1.0 -1.0 1.0 > > X4 -1.0 -1.0 1.0 > > Obviously, X1 is below the plane spanned by X2,X3, and X4, and X2->X3->X4 are > arranged clockwise, but the chiral volume calculated by the equation above is > negative (but should be positive according to the definition above). > > Also, L-Alanine has an S configuration, but the chiral volume around Calpha > (N->C(O)->Cbeta) is positive (but should be negative, see above). > > Do I do something wrong, or is there a mistake on the CCP4 website? > > I would appreciate any help/comment. > > Best regards > > Matthias > > -- > ======================================== > Prof. Dr. G. Matthias Ullmann > Computational Biochemistry > University of Bayreuth > Universitätsstr. 30, NW I > 95447 Bayreuth > Germany > > Telephone: +49-921-55-3545 > e-mail: > [email protected] > > http://www.bisb.uni-bayreuth.de/ > ======================================== > > --------------------------------------------------------------- > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/WA-JISC.exe?SUBED1=CCP4BB&A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
